DIET OF HARTLAUB'S GULL LARUS HARTLAUBU AND THE KELP GULL L. DOMINICANUS IN THE SOUTHWESTERN CAPE PROVINCE,SOUTH AFRICA

Steele, W.K. 1992. Diet of Hartlaub's Gull Larus hartlaubii and the Kelp Gull L. dominicanus in the southwestern Cape Province, South Africa. Ostrich 63:68-82.

Hartlaub's Larus hartlaubii and Kelp Gulls L. dominicanus in the southwestern Cape feed on a wide range of prey species. On average, Kelp Gulls feed on larger-sized prey than do the smaller Hartlaub's Gulls. In an undisturbed environment the preferred foraging habitats of Hartlaub's and Kelp Gulls are rocky shores and open, sandy beaches (where sand mussels Donax serra are common) respectively. However, as a result of man's activities, several new foraging habitats have become available including croplands, fishing harbours and refuse dumps. The provision of supplementary food at these new foraging habitats is likely to be the cause of a recent population increase. Kelp Gull chicks are fed predominantly “natural” prey which indicates that the population increase may not be due to enhanced reproductive success, but to improved post-fledging survival of juveniles, which are known to aggregate at sites where supplementary food is provided.     

白暨豚种群数量及资源保护

为了了解长江中白鱀豚的分布状况及种群数量,从1978年至1983年1月止,先后9次在长江中、下游(宜昌至南通)的干流进行了白鱀豚的生态考察,并到汉江和鄱阳湖、洞庭湖等水域查访有无白鱀豚活动的情况,依据考察所得资料,对长江白鱀豚群体的数量作了初步剖析。 通过考察,到1983年初为止,中游最上是在湖北枝城,约距长江口1,613公里的江段和下游最下是江苏太仓浏河口距长江口24公里的江段都有白鱀豚的活动。白鱀豚种群约156头,20个群体,分布在长江中、下游的17个江段里,在安庆一黑砂洲南水道约170公里及嘉鱼—王家渡水道约80公里的两个江段里生活着较多的个体。根据雌、雄自鱀豚体长与年龄关系式的速度变化曲线,白鱀豚的个体发育阶段可分为:幼龄期(胎儿—雄性4龄,雌性5龄),壮年期(雄性5龄—12龄,雌性6龄—13龄),成年期(雄性13龄,雌性14龄至20龄)和老年期(20龄以上雌雄个体)4个龄期。白鱀豚种群的年龄结构是一个基部较窄,顶部相对宽的锥体,显然是一个生产较差的种群。 近些年来,由于人类对江河的开发利用,使得白鱀豚种群的补充能力和再生产能力都遭到了一定程度的破坏。分析白鱀豚资源减少的主要原因是:(1)食物条件的变化;(2)有害渔具对白鱀豚的杀伤;(3)航运业务对白鱀豚的误伤;(4)群众缺乏保护珍贵动物的知识而     

HARTLAUB'S GULL: EGGS AND INCUBATION

A.J. Williams. 1990. Hartlaub's Gull: eggs and incubation. Ostrich 61:93-96.

At Marcus Island, South Africa in 1979 Hartlaub's Gulls Larus hartlaubii laid eggs between 31 January and 28 February. Clutches were of one to three eggs; and 49% consisted of two eggs. Egg composition, and intra-clutch variation in egg size and weight, are reported. The laying interval was two days, the incubation period 25 days, and the hatching interval 0,8 days.     

DISTRIBUTION,POPULATION SIZE AND CONSERVATION OF THE SWIFT TERN STERNA BERGII IN SOUTHERN AFRICA

Cooper, J., Crawford, R. J. M., Suter, W. & Williams, A. J. 1990. Distribution, population size and conservation of the Swift Tern Sterna bergü in southern Africa. Ostrich 61: 56–65.

The Swift Tern Srerna bergü occurs commonly in coastal southern Africa, with a nonbreeding distribution extending the length of the southern African coast and into southern Angola. The known nonbreeding distribubon of the nominate subspecies S. b. bergü extends from Swakomund, Namibia to Kosi Bay, Natal, South Africa. In Natal its nonbreeding distribution overlaps with that of the subspecies S. b. enigma. The species very rarely occurs inland or far out to sea. The geedin distribution of tre nominate subspecies extends from Swakopmund to Algoa Bay, eastern Cape, South Afcnca.

Twenty-two breeding localities are known in southern Africa, but usually only six to seven are occupied. in any one year. Most breeding localities are marine islands where Swift Terns often breed in muted colonies with Hartlaub's Gulls Lorus hartloubii. In 1984 a complete breeding ansus estimated a breeding population of 4835 pairs. However, 6088 pairs were counted at only three localities in 1988. The size of the annual breeding population varies by a factor of as much as 1,6; although the overall size of the adult population is thought to be reasonably stable with no temporal trends evident. Thirteen breeding localities which are legally proclaimed nature reserves supported 72% of the 1984 breeding population. Existing and perceived threats to the Swift Tern are discussed in detail. To improve further tRe conservation status of the Swift Tern in southern Africa, it is recommended that: unprotected breeding localities be proclaimed reserves, also protecting those not on islands with adequate fences; feral cats be removed from breeding islands where they are present; and fisherman be educated to release entangled terns and not to discard lines and nets.     

DISTRIBUTION,POPULATION SIZE AND CONSERVATION OF THE CASPIAN TERN STERNA CASPIA IN SOUTHERN AFRICA

Cooper, J., Brooke, R.K., Cyrus, D.P., Martin, A.P., Taylor, R.H. & Williams, A.J. 1992. Distribution, population size and conservation of the Caspian Tern Sterna caspia in southern Africa. Ostrich 63: 58–67.

The Caspian Tern Sterna caspia occurs along the whole southern African coastline and on large river systems and water bodies away from the coast. A total of 28 definite breeding localities has been recorded in southern Africa. Breeding has occurred recently at at least 14 coastal localities between Swakopmund, Namibia, and Lake St Lucia, Natal, South Africa. Inland breeding has been recorded in recent years at Sua Pan, Botswana and Kalkfonteindam, Orange Free State, South Africa. Based on censuses conducted between 1980 and 1991, the southern African breeding population is estimated to be of the order of 500 pairs, 91% of which breed coastally and 89% breed on islands. Up to 290 pairs (58%) bred at Lake St Lucia. Seventyone per cent of the 1980–1991 breeding population falls within eight nature reserves. Conservation of the Caspian Tern in southern Africa requires protection at breeding localities, including commercial salt and soda ash extraction works, against the effects of changing water levels, human disturbance and predation. Pesticide levels of addled and abandoned eggs should be measured at selected breeding localities.     

BIOLOGY OF THE BANK CORMORANT,PART 1: DISTRIBUTION,POPULATION SIZE,MOVEMENTS AND CONSERVATION

Cooper, J. 1981. Biology of the Bank Cormorant, Part 1: Distribution, population size, movements and conservation. Ostrich 52: 208–215.

The Bank Cormorant Phalacrocorax neglectus is a marine species, endemic to southern Africa. Its non-breeding range extends from Walvis Bay to Cape Agulhas. Breeding range extends from Hollamsbird Island to Quoin Rock. Its distribution is broadly similar to that of kelp beds Ecklonia maxima. A total of 44 breeding localities supports approximately 18 000 adult birds; 12 800 (71%) occur on two islands (Ichaboe and Mercury) north of large kelp beds. Adult Bank Cormorants are resident but juveniles may disperse several hundred kilometres. The species is not considered to be seriously at risk to disturbance at most breeding localities. However, modern expansion of fishing activities may affect the very large populations of Ichaboe and Mercury Islands.     

中国驼鹿种群数量及分布现状的研究

1985一1987年间,作者在中国东北大、小兴安岭林区,根据三阶抽样的原理,选择1 6块样地,设置并调查202条样带,长2476．6km,遇见309条驼鹿足迹链。由此,明确了驼鹿在中国的分布区域并确定总栖息面积为1 9万多km² ．平均分布密度为0.0519头／km²,种群数量为9955士397头(a=0．2 ）,其种群下降率年平均逃6.3 %,且呈继续下降趋势, 亟待保护。     

TIMING AND SPACING OF BROODS IN THE BLACK-HEADED GULL LARUS RIDIBUNDUS

The nests of the Black-headed Gull Larus ridibundus are closely aggregated into dense colonies and their use synchronized, these two phenomena together tending to produce a maximal clumping effect. Within such a colony however, nests were found to be spaced out to produce a non-random uniform distribution. The commonest distance between neighbouring nests was found to be about one metre, in contrast to related species. This study was concerned with two aspects of this distribution pattern; its survival value and its behavioural causation.
It was found that pairs nesting just outside the colony had a much lower breeding success than those nesting in the colony and that nests on the colony fringe had a slightly lower success than those in the centre. Pairs laying during the peak laying period had a higher breeding success than pairs laying either earlier or later in the season. Since by far the most important mortality agent was predation, it seems likely that both clustering and synchronization of nesting function as antipredator systems and arguments in favour of this are discussed.
Variations in nest-spacing within the colony were not correlated with variations in breeding success.
In the causation of the spacing between nests, territorial aggression was demonstrated to be an effective dispersion mechanism and the way in which this mechanism works was investigated in detail.
This spacing mechanism was not sufficient by itself to explain the observed densities, which were higher than one would expect from the aggression alone; there was also some tendency for birds establishing a new nest-site to cluster close to others. The interaction between this, the territorial aggression of the residents and the subsequent avoidance responses of the settling birds, can explain the nest spacing pattern and probably also the observed densities.     

有关棕头鸥和遗鸥两近似种的分类与分布问题研究

本文根据近几年的野外观察结果并分析有关文献资料,系统地比较研究了棕头鸥和遗鸥两近似种的分类和分布现状,直接依据野外活体形态并对照系列标本对两种鸥的成、幼鸟和雏鸟的形态及野外临别特征给出了较精确的描述,澄清了这两种鸥以往在分类上的混淆有分布认识上的错位,同时从生态－动物、地理和行为学的角度对两种鸥的现有分布和今后分布态势的演进做了分析论证。     

AGE, EGG-SIZE AND BREEDING SUCCESS IN THE HERRING GULL LARUS ARGENTATUS

The breeding biology of the Herring Gull Larus argentatus was studied in 1969, 1970 and 1972 on Skokholm, Pembrokeshire. The distribution of laying dates in three years is given; median laying date was always about 10 May. Laying dates of individual pairs were fairly constant between two years, but females up to nine years of age apparently advanced their laying date in successive years. In 1969 there was a decline in clutch-volume index during the season but this was not found in 1970 or 1972. Females laid clutches of similar volume in successive years, although the volume did vary with age, increasing up to 7 or 8 years of age and then declining. Hatching success was highest in the earliest of four periods in 1970 (69%) and lowest in the last (51%); in 1972 the corresponding figures were 71% and 63% and the seasonal trend was not significant. Chick mortality was higher in 1970 (69%) than in 1972 (59%); in 1970 there was significant seasonal variation in chick survival but in 1972 there was not. In 1970 chick survival was positively correlated with hatching weight (and hence egg-size) and chick survival was also related to growth which was itself correlated with hatching weight. There were no such correlations in 1972. Mean chick production in 1970 was 0.60 per pair and in 1972 0.70. In both years later breeders were less successful, but the seasonal range of mean success was less in 1972. In the discussion it is shown that some of these differences between years could be due to changes in the age structure of the population and it is suggested that the correlation between egg-size and chick survival in 1970 may be an artefact of the age structure.     

MIGRATION AND DISPERSAL OF AUDOUIN'S GULL LARUS AUDOUINII FROM THE EBRO DELTA COLONY

Oro, D. & Martinez, A. 1994. Migration and dispersal of Audouin's Gull Larus audouinii from the Ebro Delta colony. Ostrich 65:225-230.

Migratory paths and dispersal patterns of Audouin's Gulls (Larus audouinii) born in the Ebro Delta have been studied, as well as their degree of philopatry. The gulls always disperse southwards from the colony, and only the juveniles seem to disperse in other directions. Dispersal patterns of 2y, 3y and older gulls are similar, wintering mainly on Iberian Mediterranean and Moroccan Atlantic coasts. Juveniles migrate before the rest of the age classes and they winter south of older gulls, in the Senegambia region. However, conclusions on Audouin's Gulls movements are difficult to draw, owing to the large differences in resighting and recovery efforts. Data presented also suggest that Audouin's Gulls do not appear to breed before the age of four years.     

牛背梁自然保护区羚牛的分布与数量

1998 年1～4 月对牛背梁国家级自然保护区内羚牛种群数量与分布做了调查, 结果表明, 保护区内有11 群羚牛, 总数量119～130 头(包括独牛) , 整个保护区内羚牛分布密度为0.007 3～0.007 9 头/ hm² 。在冬季, 羚牛分布于海拔1 900～2 700 m的5 块相互隔离的栖息地中, 以海拔2 200～2 600 m之间分布更为集中。在1981～1998 年的17 年间, 保护区内的羚牛种群分布范围在逐渐缩小; 从上世纪50 年代至90 年代, 羚牛最低的分布高度比历史分布高度至少上升了400 m。周边地区人为干扰、生境不断丧失和保护区内生境破碎化是导致羚牛分布现状最直接的原因。     

SPECIES ISOLATION BETWEEN THE HERRING GULL LARUS ARGENTATUS AND LESSER BUCK-BACKED GULL L. FUSCUS

There is a large, mixed colony of the two “ring” species, the Herring Gull Larus argentatus and Lesser Black-backed Gull L. fuscus, on Walney Island, northwest Lancashire. These birds are nesting at the very high density of one nest/40 square yards, or more, but although they defend their territories against both species indiscriminately, there is effectively no hybridization. This paper discusses the nature of the species isolation mechanism, and its function. Since the two species can produce fertile hybrids, the mechanism must be of an ecological/behavioural nature, rather than morphological incompatibility. It is shown that there are slight differences in breeding season and habitat, but these do not seem to be great enough to account for the high degree of isolation. It is likely that species isolation depends primarily on the female's choice of a mate. It is suggested that, as specific cues, she uses the differences in call-note tones, and the colour of the back (and perhaps also of the eye-ring), or both. Herring Gulls and Lesser Black-backs are adapted to slightly different niches. The overlap is so great, however, that any hybrid is unlikely to be at a disadvantage; but the overlap can only have arisen very recently, as a result of both species taking advantage of the increased availability of human refuse. It is possible that the isolation mechanism was evolved to cope with earlier conditions, when food was more limited, and the species' niches more sharply defined.     

NESTING DENSITY AND BREEDING SUCCESS IN THE HERRING GULL LARUS ARGENTATUS

The relationship between nesting density and breeding success of Herring Gulls Larus argentatus was studied on the Isle of May, Scotland, in 1968. Herring Gulls nesting at the most common density started laying earlier in the season than those nesting at lower or higher densities. Therefore, although the overall spacing of nests was uniform, the nest density of birds laying later in the season progressively approached a random distribution. The onset of laying occurred in synchronized groups within the colony. Late-laid clutches were commonly situated on the periphery of the colony where the density of nests was lowest. When the laying period was divided into four time periods, in each period the tendancy was for birds nesting at the most common density to have the highest clutch-size, hatching and fledging success, and to rear the most chicks per pair to fledging. In addition, birds which spaced their nests most uniformly, presumably as a consequence of territorial behaviour, were the most successful parents.